This might be the best excuse for a fall family vacation we've ever heard. In honor of the National Park Service's second century of operation, you can visit any of the 417 designated areas for free on September 30.Sure, most of the parks are free year-round, but on National Lands Day, the NPS is waiving fees for more than 100 that normally charge admission. That means you and the family can plan a trip to one of the country's top outdoor destinations—for free. Travel to the Centennial State for peak family fun at Rocky Mountain National Park. Make your children's California dreams a reality by taking in the waterfalls at Yosemite. Or embark on an Arizona adventure at the Grand Canyon National Park. Whether you enjoy one of these gorgeous views or choose another from the list, the memories made will truly be priceless. (h/t Mental Floss)